Rolling-element bearings are often used in critical applications, wherein their failure in service would result in significant commercial loss to the end-user. It is therefore important to be able to monitor a bearing so that the residual life of a bearing may be predicted in order to plan intervention in a way that avoids failure in service, while minimizing the losses that may arise from taking the machinery in question out of service to replace the bearing.
The residual life of a rolling-element bearing is generally determined by fatigue of the operating surfaces as a result of repeated stresses in operational use. Fatigue failure of a rolling element bearing results from progressive flaking or pitting of the surfaces of the rolling elements and of the surfaces of the corresponding bearing races. The flaking and pitting may cause seizure of one or more of the rolling elements, which in turn may generate excessive heat, pressure and friction.
In order to improve maintenance planning, it is common practice to monitor the values of physical quantities related to vibrations and temperature to which a bearing is subjected in operational use, so as to be able to detect the first signs of impending failure. This monitoring is often referred to as “condition monitoring”.
Condition monitoring brings various benefits. A first benefit is that a user is warned of deterioration in the condition of the bearing in a controlled way, thus minimizing the commercial impact. A second benefit is that condition monitoring helps to identify poor installation or poor operating practices, e.g., misalignment, imbalance, high vibration, etc., which will reduce the residual life of the bearing if left uncorrected.
Typically, individual sensors are attached to a bearing. Such individual sensors can however take up considerable space and be difficult to connect to fixed measurement equipment because the sensors may need to be mounted a rotating surface of the bearing, such as on a rotating inner ring in order to measure the vibration or temperature thereof.